Schematic atomic structure of relaxed 1CaTcO3/1BaTcO3 superlattice at theoretical DFT ground state with monoclinic space group symmetry Pc.
Schematic atomic structure of relaxed 1CaTcO3/1BaTcO3 superlattice at theoretical DFT ground state with monoclinic space group symmetry Pc.

A group of theoreticians have demonstrated that the key to producing a room temperature multiferroic may lie with a new family of perovskite materials.

Often described as the “holy grail” of data storage, room temperature multiferroic materials have been at the forefront of functional materials research for two decades. And the reason is that they are ‘adaptable’. Multiferroic materials simultaneously exhibit two often contradictory properties – they can be both electrically charged (ferroelectric) and maintain a permanent magnetic field (ferromagnetic). In principle at least, it is possible to control the magnetic phase of multiferroic materials with an applied electric field, and to control their electric polarization with an applied magnetic field.

A collaboration of Chinese and US scientists now report that by inducing structural distortions in a specific family of perovskite superlattices, it is possible to create a new room-temperature multiferroic. Published in Computational Materials Science [DOI: 10.1016/j.commatsci.2014.09.011], the paper describes the first-principles approach used by Xifan Wu and his colleagues to explore the functionalities of this material group, ATcO3 (A = Ca, Sr, Ba). In 2011, ATcO3 was experimentally shown to be antiferromagnetic. In this work, density functional theory investigations of the structural instabilities in perovskites found that a mismatch between BaTcO3 and CaTcO3 could induce ferroelectricity at the interface. The researchers also found that the Néel temperature of their superlattice - that is, the temperature above which ferromagnetic order is lost - is 816K, making this theoretical material a multiferroic at room temperature.

A mismatch between two different materials can be induced either because of epitaxial strain – a result of different lattice spacing between crystals - or by “engineering” the interface. Earlier work has shown that epitaxial strain in perovskite superlattices can result in ferroelectricity. But Wu and his team used a thorough theoretical approach to demonstrate that enhanced ferroelectricity can be induced by interface engineering. The Néel temperature of both BaTcO3 and CaTcO3 is well above room temperature, meaning that the superlattice maintains its unique magnetic ordering and ferroelectric properties at vastly-elevated temperatures relative to most multiferroics.

This paper presents a theoretical approach, so the team now await experimental confirmation of their results. If successful, this discovery may lead to a material whose magnetic properties can be easily controlled at room temperate, and, eventually, to a new generation of extremely low-power magnetic storage devices.

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